A “fistula needle” is a large bore needle, commonly 14 to 17 gauge, which is bonded to a section of medical grade tubing used to connect the fistula needle to an extracorporeal blood circuit for use in hemodialysis.
Hemodialysis is one of the primary treatments for patients with kidney failure. These life-sustaining treatments typically require 3 to 4.5 hours each and may occur three or more times a week. However, due to differences in protocols, techniques, or varying patient needs, some hemodialysis treatment may last six hours or even overnight.
The most common access to the vascular system during hemodialysis, for chronic patients, is through use of a large gauge needle inserted through the skin into an arterial/ventricular graft, an implanted shunt or an implanted receptacle.
During a treatment, the patients' blood is processed by a filtering device commonly called a dialyzer or hemodialyzer. The blood travels to and from this filtering device through an extracorporeal blood circuit by the action of a blood pump. Every hemodialysis unit is required to have certain alarms (AAMI RD5-3.3.6) that monitor conditions throughout a treatment to insure patient safety. These alarms include temperature, dialysate pressure, transmembrane pressure, blood circuit pressure, conductivity, blood leak, and blood circuit air embolism protection.
Blood travels out from the body through the arterial fistula needle to an arterial bloodline. The arterial blood is then pumped through the bloodline, into and through the filtering device, and returned to the body through the venous bloodline attached to the venous fistula needle. As used herein, the term “venous” it is intended to mean “returning to the body” and the term “arterial” is intended to mean “coming from the body”. These fistula needles are commonly taped in place on the patient's skin near and around the access site.
One or both of the fistula needles are occasionally dislodged or removed from the access site during a treatment. Some examples of how this hazardous situation may occur unintentionally include the bloodlines getting caught on the treatment chair during a positional change such as reclining from a seated position or siting up from a reclined position. Dislodgment may also occur when clothing or blankets brush against the fistula needles and tapings during normal movements. Sometimes someone moving past catches the bloodline with a foot, a walker, a wheelchair or a cart. It may even happen when the tape on a patient simply comes off, due to dry or sweaty skin, and the needles slip out. Intentional removal of the needle(s) during treatment is also not unheard of, requiring many of the more mentally or emotionally unstable patients to be restrained during treatments. Other patients move around frequently and the many little tugs on the bloodline and tapings, and the constant pulling eventually loosens that tapings to the point that they come off and the fistula needle falls out.
Should the venous needle become partially dislodged during a treatment, the patients' blood may infiltrate (into the surrounding tissue areas), usually causing great pain, or it may leak out around the needle entry site, or a combination of both.
Should the venous needle become completely dislodged during a hemodialysis treatment, the patients' blood is not being returned and the blood is effectively drained out. With typical blood pump ranges of 50 to 650 ml/min., the blood loss may be very rapid. This situation requires an immediate medical intervention response to prevent severe patient injury or death by exsanguination. Obviously, even the most observant and dedicated of medical staff could not possibly watch each patient all of the time.
Currently, the primary device to monitor for a venous needle dislodgment is the venous pressure monitor (VPM). Under certain circumstances, VPM is not a dependable indicator for a venous needle dislodgment because the VPM may not “see” a change beyond the standard alarm limit range (50 ml/min.). This may be exacerbated when the alarm limits are not set “centered” around the varying average pressure. Significantly, the VPM will often fail to register a sufficient pressure change (to set off an alarm) due to the inherent “back pressure” developed in a venous blood line by the resistance of the viscous blood traveling through the relatively small orifice of the fistula needle.
One attempt to solve the partial dislodgment problem is offered by Shaw in his U.S. Pat. Nos. 3,618,602 and 4,010,749. These basically use the increase in skin temperature to determine the presence of an infiltration. This solution has limitations in that it is rather slow to respond as it is dependent on the reaction of the body to the problem. Additionally, it fails to address the present concern of dislodgment. While an infiltration is painful, may require surgery to correct and could even result in the loss of the limb, it is not immediately life threatening.
One proposed solution to the complete dislodgment problem is attempted in U.S. Pat. No. 6,077,443, entitled “Method and device for monitoring a vascular access during a dialysis treatment”, issued to Goldau, Rainer, which monitors the impulses (natural or added) detectable in an extracorprial blood circuit. This method has not experienced commercial success, or widespread utilization. It is believed this may be because the pressures illustrated appear to be on a very still patient, which is not a realistic assumption throughout a four-hour or longer treatment. Even very small arm movements can set off the VPM without dislodgment of a needle because of the natural pressures inherent in the needle as described above.
There are a number of sensor designs that use the inherent conductivity of blood and other fluids to set off an alarm, most commonly used in a diaper to indicate a soiled condition.
A “System for use in detection of electrically conductive fluids” was suggested in U.S. Pat. No. 5,790,036, issued to Fisher, et al., which uses the inherent conductivity of body fluids and wastes to set off an alert in a diaper. This arrangement does not adequately protect a patient as it could have a sensor failure or disconnect without alerting the staff of the sensor failure or disconnection. Additionally, the device does not explicitly provide for compliance with the nonisolated patient connection requirements of Safe Current Limits for Eletromedical Apparatus as required by Applicable Document 2.3.
U.S. Pat. No. 5,779,657 to Daneshvar entitled “Nonstretchable wound cover and protector” shows and describes a simple blood leak detector. The soiling of a gauze pad with blood would complete a circuit, allowing an alarm to sound. As in the case of the Fisher unit, Daneshvar's unit fails to alarm in the case of a sensor failure. Daneshvar's unit also is not compliant with the nonisolated patient connection requirements for electrically sensitive patients. Additionally, whether Daneshvar's unit will alarm depends on the absorbency of the gauze, which may be compromised due to being saturated by non-conductive fluids or by compression, or coated by certain medical gels, pastes or ointments.
The devices described in WO 99/24145 and U.S. Published Patent Application 2002/0198483 A1 attempt to detect a separation of the extracorporeal circuit. However, neither of these allow for an unobstructed view of the access site. Another problem they share is that they are designed for use as an integral part of a dialysis machine. As such, they are specifically not designed for stand-alone use. Of greater concern is the failure of any of these devices to fail in a safe manner. If the unit fails for some reason, such as a dead battery, the protection is lost and the staff is not aware of it. While both of these references indicate that they determine needle dislodgment, they really are mere variations on the wet diaper sensor idea in that they only detect blood or other conductive fluids. They are not actually determining the needle position. With some of the newer implanted tubing and other new types of vascular accesses, there is very little bleeding when a needle is removed, and, hence, limited opportunity for success in alerting the staff in the case of a rapid needle withdrawal, such as when a bloodline is caught by a passing foot, or when a mentally unstable patient intentionally removes the needle. Additionally, in applications other than dialysis, the underlying region or substrates may not have a sufficient positive relative pressure to force out blood, body fluid or liquid to wet the sensor.
The reusable sensors described in the references mentioned above and elsewhere in the prior art involve the myriad of problems and costs associated with reusing soiled medical equipment including, but not by way of limitation, sterilization, clean storage, verification of the absence of the sterilant prior to use, reused devices being reused only by the original patient, quality problems due to subjective assessments, etc.